It is broadly known to provide latch or fastening structures in or on a sliding window sash for the purpose of holding the sash in any of several partially open positions. Such structures have long been used in windows in railway carriage cars, busses and buildings for the purpose of adjusting the amount of ventilation which the window provides. Examples of such structures are described in U.S. Pat. Nos. 429,669, 2,018,281, 2,547,315 and U.S. Pat. No. Re. 24,077.
With respect to storm windows it has been recognized that the space between a storm window and its prime window occasionally requires venting in order to remove condensation which may have occurred in that space. The present invention is particularly directed to providing for circulation of outside air in that space. It was thought at first that providing a closable vent slot or slots directly through the storm window sash would be a suitable arrangement for effecting the desired air circulation. However, later calculations showed that such an arrangement was not satisfactory for a tightly fitting storm window which permits only very little air to leak from the outside into the space between the storm window and the prime window. Specifically it was shown that the total area of the vent or vents necessary for effective condensation removal was so large that it would require so large a vent or so many small vents as to be impractical. Therefore it was decided to provide venting by arranging for the lower sliding sash to be propped in a partially open position when desired. The prior art window latching or holding devices, such as those described in the aforesaid patents, are not readily incorporated into a sliding storm window sash because they tend to be inaccessible to the operator or to interfere with proper operation or sealing of the sash.
The present invention provides a simple and conveniently operated sash holding device which comprises at least one stop member carried within a downwardly open recess in the lower horizontal sash member and mounted in the recess for free sliding movement in vertical directions. In its down position the stop member protrudes out of the recess to engage the lower window frame member or sill and is latched in that position so as to hold the sash in a partially open position. In its up position the stop member resides in the recess. The mechanism for latching the stop member includes a manually operable member carried by the horizontal sash member.
In the embodiment described more in detail hereinafter the assembly is constructed and arranged such that upon raising the sash the stop member automatically moves to its extended or down position and upon closing the sash the stop member is pushed up into the recess in the sash by engagement of the stop member with the window frame or sill. That is, when the latch member is in its inoperative or "closed" position the stop member is functionally inoperative to hold the sash up, even though the stop member moves. If it is desired to prop the sash in a partially raised position the sash is first raised to at least that position and then the latch member is manually moved to its operative or "open" position to prevent the stop member from moving upwardly.
The latch member thus has only a single latching position, in the sense that it does not latch the stop member in an up position. This feature renders the structure of the assembly of latch member and stop member mechanically simple yet provides the operator with simple and easy control. As the normal position of a lower storm window sash is a down or closed position and as the sash is seldom raised, there is no need to provide for latching the member in its up position. The preferred form of latch member is a horizontally slidable plate or the like fitted into the sash and having a finger hole to receive one or more of the operator's finger tips. It is mechanically and functionally simple to arrange for the plate or the like to have a first or "closed" position in which it does not cooperate with the stop member and a second or "open" position in which it latches the stop member in its down position.
The venting assembly of the present invention, being associated only with the lower horizontal sash member, is particularly useful with a storm window which includes vertically movable sash retainers, because the assembly does not interfere with or require modification of the sash retainers. A storm window of this kind is described in U.S. patent application Ser. No. 109,408 filed Jan. 3, 1980 now U.S. Pat. No. 4,283,883.